Television system



June 23, 1953 G. c. szlKLAI 2,643,239

.TELEVISION SYSTEM i x Filed Aug. 31, 1949 Ys sheets-sheet 2 INVENTOR Georgegzldl June 23, 1953 G. c. szlKLAI 2,543,239

TELEVISION SYSTEM Filed Aug. 51, 1949 3 Sheets-Sheet 3 5 I A [33 t 6166 V3 I l I ..0 z

ifi-@@@ INVENTOR Patented June 23, 1953 UNITED :STATES ATENT OFFICE T'EL'EVISION SYST M* .Delaware y13 Claims. 1

This invention Yrelates to 'a system land method for simultaneously transmitting a plurality of sets of information and 'may :be useful .in fcolor television.v

It is highly vdesirable that color television "sys"- tems be compatible with .present television `standards in order that the present monochrome receivers, which lproduce black Iand white images, will not be made obsolete.

In order to make eiiicientuse of the "frequency band that maybe available, it is Apossible to transmit a single voltage wave that is coded so that it contains simultaneous information as Y.to 'the relative intensities of the component colors Arequired to produce a colored image. Were it not for the requirement of compatibility and for the distortion usually ypresent 'in any `transmitted voltage wave. various values of the transmitted voltage wave could 'beassigned at random to the ratios of component Ycolor intensities.

However, it 'is :obvious that the transmitted voltage wave must substantially conform to the light intensity in the scannedobject if black and white receivers "now in use are to 'reproduce an acceptable black `and white image .from the coded transmission. g

Noise, multipath and other sources 'of interference produce distortion inthe transmitted volt age wave and make 'it necessary to have proximate values of the transmitted wave `correspond to color shades that :are very much alike. lOtherwise, a slight distortion might, xby way of illustration, cause the 'receiver to produce fred vwhen the actual scene was green.

This invention makes possible the transmission of colored images in such manner `that the requirements of Acornpatibiiity and freedom from color dilution inthe presence 'of distortion are adequately met.

Briefly, this 'is achieved by .coding the transmitted wave within predetermined levels in such manner that as the wave increases, the intensity ef a iirst color component decreases while the intensity of another component increases. When the transmitted Wave passes 'through another predetermined level, the intensity of only one of the color components is increased. -From this point to the next :level the intensity o-f the first color is gradually increased While the intensity of the other color is decreased. Y

As applied to a color ,receiver built in accordance with the teachings of this invention, -this means that the overall intensity of `the vrepro-f duced colored .image will remain constant fin 'the region between each se't of levels. iis so -b'e- `cause lthe reproducer's 4of each component fcolor are operating `'continuously 'so that `'the intensity of their combined images is necessarily equal to the sum of 'their `individual intensities. vHowever, the color shades can b'e varied within each range. At the end cfa range the intensity vof the image formed by a reproduc'er `of one of the component colors is increased s'othat'a new intensity level is reached.

As applied to `receivers now in use, the black and Whiteimage that "they reproduce in response to ea transmitted wave that is coded Vin accord'- ance 'with the `tea'ol'iings `of this invention changes iin intensity as the transmitted wave 'changes in value and., therefore, vitsintensity is `not constant fas the value of the transmitted wave passes through any-given range, :but this is not harmful providing there `is not too 'much difference be'- tween the rsignal levels at the ends of a range.

JAccor-ding toanother aspect .of the invention, it is possible to transmit pleasing colored images with fewer intensity levels 'by 'eliminating certain color combinations.

,Although 'the invention is illustrated by reference to a color television system, it will be afpparent to those skilled in the art that the novel principles-disclosed may be employed in the transmission of kany desired vsignals whether they are relatedor not. Y

The object of the invention is therefore to provide an improved means and method whereby a "plurality of signals `can be simultaneously trans- `mitted with maximum fidelity 'in the presenceof distortion lof the transmitted signal.

A still further object of the invention is to provide an improved means and a method whereby the number *of levels necessary to 'produce a pleasing colored image may be `substantially reduced.

Another `object "of theinvention is to transmit video signals so that they `can be reproduced .in black and white by standard receivers with mini- `mum errors in brightness vvand at the same time be reproduced in color `b'y 'receivers lconstructed in Laccordancewi'tlfi this invention with minimum Icolor dilution.

These and other objects willbe apparent from 4a vconsideration of the following iigures in which.:

Figure 1 illustrates fla `code for 'use with signal transmission 'systems that is the subject -of this invention;

.Figure 2 shows 'atra-n'smission system including a special tube for coding 'information in accord'- ance with this invention;

Figure 3 shows in yschematic form a 'receiver Y 3 adapted to analyze the code of this invention; Figure 4 shows the target used in a special cathode ray tube at the receiver for analyzing a signal coded in accordance with this invention;

Figure 5 illustrates an alternative type of target that may be used in a coding tube;

Figure 6 shows a circuit for decoding the signals at the receiver;

Figure 6A illustrates the operation of the device shown in Figure 6;

Figure 7 shows a type of target for use in a special coding cathode ray tube that permits a reduction in the number of levels of brightness; and

Figure 8 shows the type of target used in a receiver when the signal is coded in accordano with the target shown in Figure?.

Reference is made to thercoding system ofY this invention, as illustrated in Figure l, in which thel successive levels of signal intensity, indicated by vthe numerals within the small rectangles, proceed back and forth along the diagonals of the larger rectangle within which they are enclosed. rhe 'intensity of the green component increases in a downward direction and the intensity of the red and blue components increases to the right. The horizontal position is first representative of the blue content and then of the red, vas those two colors may be multiplexed in any known fashion. The eect of noise or other distortion on such a code can be appreciated by assuming, for example, that the true level of the transmitted voltage wave corresponds to the level Il and that distortion changes it to a level I8. Only a small amount of color error is thus introduced as the i vreci and blue content drops from the third level to the second, and the green increases from the second level to the third. Thus, the probability of going from one saturated color to another is substantially eliminated. Furthermore, the total intensity or brightness of the colored image remains constant within a predetermined range as the sum of the red, blue and green components -is the same, the loss in red and blue intensity being compensated for by the increase in green intensity.

For purposes of convenience, each of the suc- Y ycessive levels of the signal, as represented by the numerals within-each small rectangle, is hereby defined as a `color-brightness level, as it represents a unique combination of the intensities of the component colors. In the central area of the rectangle a change in the color-brightness llevels represents a given increase in intensity of one component color and a similar decrease vin another so that the total brightness produced by the different colors remains substantially the same. At the edges of the system of targets, however, where either of the color components vis either zero or saturated, a change in the colorbrightness by one level may cause one color alone -to change in intensity without changing the other so that a change in the total brightness level is 'brought about. Thus, levels l and 2 are in a first total brightness level, 3` through 5v another, etc.

zontal and vertical rows, as indicated in Figure 1. Each target 24 may be connected in parallel to a common output lead 2t in such fashion that the response Vto the electron beam is proportional to the level indicated by the numbers in the small squares of Figure l. In other words, each small rectangle in Figure 1 corresponds to a target which kprovides a signal to lead 26 in the presence ofthe beam that is proportional to the number therein. The means for producing a signal required by the code at the various targets may comprise potentiometer '28 as shown or properly biased amplifiers connected between each target 24 and the lead 25.

The green video signals are connected to the vertical deflection plates IS via lead ll and deiiect'the beamV downward as the green intensity increases. The red and blue signals are alternately supplied to the plates I8 by multiplexer cpo 34 via lead 36 so that the beam is deflected to the right as' the strength of the red or blue signals increases; In order to insure the beam hitting the upper left-hand square of Figure 2 when no signal is present on either set of plates, biasing potentiometers 3i and 38 may be provided. The beam is accordingly `brought to a coordinate position determined Vby the intensities of the signals supplied to the two sets of defiecting plates, and a voltage of a level corresponding to the numeral within that target struck by the beam is supplied to output lead 26. The output lead 2G is connected to any suitable transmission system.

Apparatus and methods of receiving and decoding the signals transmitted as described above are now discussed. The signals supplied bylead 26 to the transmission system may be detected by any standard receiver t2 shown in Figure 3 and supplied to another special cathode ray tube 43 which is used to decode the signal.

The tube 63 comprises an envelope lill, an electron gun @6, a control grid 13S, and electron beam deflection plates '52. The electron beam formed by the gunY it .is a flat horizontalv type such as may beproduced by the gun structure disclosed in U. S. Patent No. 2,434,713 issued on January 20, 1948 to Mueller, and is moved up and down by the signals applied to the deiiection plates E2 so as to scan the targets 53 and 5d, illustrated lin detail in Figure 4.

The targets may be two separate vertical strips, strip 53 being connected to the green image reproducing channel 55 and strip 54 being con.n nected to multiplexer 56 which successively apE plies the signal to the red reproducing channel 57 and the blue reproducing. channel 58. A mask 60 is placed between the targets or strips 53 and 54 and the gun 46 so as to permit a desired por tion of the electron beam to strike the targets at vertical positions determined by the received signal.v A biasing means 62 is connected to the plates 52 so that'the beam is at its uppermost position indicated vby the numeral zero when no signal is present. Y

Upon receipt of the signal having an amplitude of one unit, for example, the beam is moved down to the level on the target indicated by the same number so as to pass'through the aperture 6&3 in the mask 60 that is located opposite the red and blue target 54. If, on the other hand, a signal having an amplitude of e isV applied to the deflection plates 52, the beam is deflected to a positionopposite numeral i in Figure '4, and both targets 53 and 54 are struck by the electron beam through apertures 66 ,and 68.l

The magnitude of the signals provided by the targets 53 and 54 in response to the electron beam is determined by the horizontal dimensions of the apertures. For example, it will be Y noted that the apertures 'IIi and 'I2 at levels 3 and 5 respectively are twice the size of the apertures shown at level I. Inasmuch as twice the width of beam strikes the targets 53 and 54 through these apertures, twice the amplitude of signal is provided to the control electrodes of the partial image reproducing cathode ray tubes. Thus, in accordance with the code shown in Figure l, level 3 corresponds to 22 percent green intensity and level 5 corresponds to 22 percent red intensity. Y

Figure 5 shows a target 'I4 and a mask is that may be substituted for the target 24 shown in Figures 1 and 2 in such manner as to eliminate the necessity for a plurality of circuits being tied in parallel t the output lead 26. The target 'hi is a single sheet of conducting material and is connected to the output 25 by a single lead la. Various areas of the mask 'I6 correspond to rectangles 24 of the target 25 shown in Figures l and 2 and each of these areas is perforated so as to allow more of the electron beam to reach the target i4 as the color-brightness level indicated by the code in Figure 1 increases in value. In other words, a single opening may be provided for a color brightness level I and two such open- Y ings provided for color-brightness level 2, etc.

nected to the multiplexer 5B. Each of these channels is comprised of a plurality of stages that produce an output signal that increases during one range of input signal and decreases during the next. Stages in the two channels that operate during successive ranges fof applied signals are so biased as to produce outputs that are 180 degrees out of phase. This means that the output of one channel is increasing as the output of the other channel is decreasing as is required. For purposes of simplicity, only two stages of one channel are shown and described.

A signal coded in accordance with the teachings of this invention is supplied via channel input lead 'do to the grids of amplifiers 8| and 82. Amplifier is cathode coupled by common resistor dfi to amplier 82 and its plate 85 and the plate de of amplifier 8l are tied together through a common load impedance 81 to a source of xed B+ potential.

These elements constitute a lrst stage which operates as follows: When no signal is present on lead 80, tube .SI is biased to cut-olf and tube 82 conducts suinciently so that the voltage at the plates 85 and 86 may be half the B+ value. As the signal increases through the rst range (E1- E2) of Figure 6A which would be levels I and 2 of Figure 1, the increased conduction of tube 82 gradually increases the bias on tube 83 with the result that the plate voltage gradually increases to B+, as shown in Figure 6A. At the beginning of the second range (E2-Es) the bias established at the grid of tube 8l by a source of fixed negative potential 88 is overcome and tube SI begins to conduct with the result that its plate voltage gradually decreases to a minimum point determined by saturation. I'his alternat- 6 ing voltage is coupled by condenser .89 to a common output lead 9B of the channel that is, in turn, connected to channel 55 of Figure 3.

Other similar stages are connected in parallel with the one described as generally indicated by numeral 9|. The biases are so arranged that the voltage relationships are not changed until the tube in the previous stage corresponding to tube 8I is saturated, at which point it operates in a manner just described. The other channel is comprised of a similar group of stages that are biased so as to operate as indicated by the dotted line of Figure 6A. Thus, as the output of one channel is alternately increasing and decreasing, thenoutput of the other channel is alternately decreasing and increasing in accordance with the code.

For the purpose of reducing the number oi. levels of color-brightness required, a target such as illustrated in Figure 7 may be employed at the transmitter in place of the target 24 shown in Figures 1 and 2. Instead of 100 levels of colorbrightness there are only 24. A compromise is therefore made in that there are not as many combinations of the intensities of the component colors, and certain color intensities cannot be obtained in a highly saturated condition but must be combined with various intensities of another color.

The inner targets are rectangular or diamondshaped with their diagonals running horizontally and vertically with respect to the target as a Whole. The triangular niches between the outer diamonds and little areas beyond may be lled in with targets of a shape approximated by superimposing a triangle on a rectangle in such manner that one side of each coincides. Coded signal responses are obtained in the same manner as was explained in connection with Figures 1 and 2.

Referring again to Figure 7, the numerals Within the diamonds correspond as before to the level of the signal to be produced when the electron beam strikes a particular target. The unshaded targets represent those intensities of the component colors that can be obtained in a highly saturated condition and combinations of these. For purposes of simplification, these targets are located at intersections of the even numbered coordinates. However, intersections of the odd numbered coordinates indicate shaded targets that cannot produce their corresponding intensities in a single component color but only in combinations with each other. Thus, 16.7 percent green can be obtained in combination with 16.7 percent, 50 percent and 83.3 percent of red or blue, but cannot be obtained by itself.

In this way, four highly saturated levels of green or red and blue may be obtained, but three additional levels of each are available with slight dilution.

At the receiver, the signal thus transmitted is decoded by a special cathode ray tube that is similar to that illustrated in Figures 3 and 4, the target and mask of Figure 8 being substituted for the target of Figure 4. The targets 93 and 95 for such a tube are shielded by a mask'i which has no openings opposite zero level, two single openings opposite level 2, etc. so that the amount of the flat horizontal beam that is permitted to reach each target is proportional to the level of the green and red or blue represented by the coded voltage wave.

For the sage of simplicity, variations in construction Voi apparatus -for coding'signals in accordance with the principles of this invention have not previously been discussed, but a few of them will now be explained.

Y Instead of using a special transmitting tube having a plurality of targets, it is possible to employ an ordinary cathode ray tube, 4by placing an optical wedge between the face of the tube and a photoelectric cell that is coupled via output lead 25 to the modulator. If the wedge is properly shaded at the various coordinate points on its surface, the light produced by the fluorescent material on the face of the tube may be modulated in accordance with the `desired code. For example, ii a Wedge were used in connection with the code of Figure 1, it would range in light transmission 'qualities from black in an area corresponding to the small square -containing the numeral to transparent at square bearing numeral 99.

'A similar device could be used as a decoder at the receiver `as it would only be necessary to deflect a iiat ribbon beam in one direction in response to the level of the received signal and to permit an amount of light to pass that is proportional to the amount of beam that Agets through the apertures in masks 60 and 91. Of course, it would be necessary to substitute two separate photoelectric cells for the targets 93 and e5, one connected to the means for forming the green content of the image and the other successively -connected to the means for forming the red content of the picture and the means for forming the blue content of the picture.

Although such systems are more easily understood when explained in rel-ation to amplitude modulation,v the invention is not limited to any particular type of signal transmission. For example, if frequency modulation were employed,

the various levels correspond to levels of fre- Y quency, and if phase modulation is employed, the levels would refer to various levels of phase. It may be desirable to pulse or sample the information to be transmitted, in which case a source of sampling signals 99 may be connected to the grid i4 of a coding tube of the type shown in Figure 2 and to the multiplexer 31S. At the receiver a source of similar sampling pulses i0! may be connected to the grid 43 of the decoding tube 43 shown in Figure 3 and to the multiplexer 56. It will be apparent to those skilled in the art that whether or not this is .done will not impair the advantages to be derived by employing the methods herein described.v vThis invention is a marked step forward in the art of -signal transmission because it allows two separate signals to be transmitted in Asu-ch manner that any distortion of the signals produces a minimum effect on either. As applied to color television, this means that errors in color and brightness are reduced to a minimum and, at the same time, that images reproduced from said signals by present blackand white receivers will be of high quality. Y

Having described my invention, I claim:

1. An apparatus for transmitting at least two sets of intelligence comprising means for derivn ing a rst voltage wave corresponding to a rst intelligence, means for deriving a second voltage wave corresponding to a second of intelligence, electronic means adapted to develop a third voltage wave in response to said iirst and second voltage waves such that increasing values of said'third voltage waves represents an increase in the sum ofr said lirst and second voltage waves Y d in a step fashion as well as the ratio between them.

2. A color transmission system in which a number ofV different colors of diiferent brightness and saturations are transmitted compris-V l ing a means for Vdeveloping a first voltage wave having a characteristic thereof varied in accordance with a irst color content produced by scanning an object, means for developing a seoond voltage wave having a characteristic thereof varied in accordance with a second color content produced by scanning the object, and means for assigning successive values of a given characteristic of a third voltage wave in such manner that successive groups of values correspond to successive total brightness levels, and each successive value represents a change in one color in one direction and a change in the other color in the opposite direction.

3. A system for transmission of a plurality oi signals comprising a means for developing a first signal corresponding to a first intelligence, a means for developing a second signal corresponding to a second intelligence, means responsive to the iirst and second signals so as to provide a thirdV signal having a characteristic thereof variable through va plurality of values, each of said values corresponding to a predetermined combination of the magnitudes of said rst and second signals, said combination being such that adjacent values indicate changes in one signal in one direction and changes in the other in the opposite direction except where the change is in such a direction as to decrease one of said signals below zero or above its maximum, in which case the other of said signals alone is changed.

A system for transmitting a plurality of conditions of color-brightness comprising a first source adapted to produce voltage waves having a characteristic thereof varying in accordance with the intensity of a first primary color as an object is being scanned, a second source adapted to produce voltage waves having a characteristic thereof varied in accordance with the intensity of a second primary color as an object is being scanned, a third source adapted to produce voltage waves having a characteristic thereof varied in accordance with the intensity of a third primary color as the object is being scanned, coding means for developing a coded voltage wave in response to said voltage waves, each level of said coded wave representing a particular colorbrightness determined by the voltage waves produced by any two of said sources, means for connecting the output of the iirst of said sources to said coding means, means for successively connecting the outputs of the second and third sources to said coding means.

5. An apparatus for transmitting colored images comprising a rst means for deriving video signals related to a first color, a second means for deriving video signals related to a second color, a cathode ray tube, an electron gun mounted in one end of said tube, a rst beam deiiecting means, a second beam deflecting means, connections between said rst means and said iirst beam deecting means, connections between said sec'- ond means and said second beam deflecting means, a plurality of targets mounted Within said tube, and means associated with each of said targets for developing voltages, in response to electrons from said gun, of different levels of increasing value starting at one corner target and progressing back and forth along the diagonals of therectangle,...

6. An apparatus for decoding a signal having different values thereof corresponding to different combinations of the magnitudes of at least two functions comprising an input circuit to which said signals may be applied, a first output circuit, a second output circuit, means connected between said input circuit and said rst output circuit for conducting energy therebetween, said means being adapted to conduct increasing amounts of energy vas said signal increases within a given range, means connected between said input circuit and said second output circuit for conducting energy therebetween, said latter means being adapted to conduct decreasingamounts of energy as said signal increases within said given range.

7. An apparatus for decoding a signal having different values thereof corresponding to different combinations of the magnitudes of at least two functions comprising an input circuit to which said signals may be applied, a rst output circuit, a second output circuit, means included in said first output circuit for controlling the energy flowing therein in response to the signals applied to the input circuit, said means being adapted to conduct increasing amounts of energy as said signal increases within a given range, means included in said second output circuit for controlling the energy llowing therein in response to, said signals, said latter means being adapted to conduct decreasing amounts of energy as said signal increases within said given range.

8. A coding tube comprising an envelope, an electron gun adapted to project a beam of elec'- trons mounted within said envelope, means for defiecting said beam in a horizontal direction, means for deflecting said beam in a vertical direction, a plurality of targets mounted within said envelope, said targets being located at points determined by a system of horizontal and vertical rectangular coordinates, and leads from each of said targets extending through the envelope.

9. A coding device comprising a coding tube such as described in claim 8 in which means for developing a signal of a predetermined magnitude are connected to each of said targets, said means being so adjusted that signals of increasing value are produced as the electron beam deected in a given direction along targets located on one diagonal of said rectangular coordinate system, and signals of increasing value are produced as the beam is deflected in the opposite direction on an adjacent diagonal.

10. A coding device comprising a coding tube such as described in claim 8 in which means for developing a signal of a predetermined magnitude is connected to each of said targets.

11. A decoding tube comprising an envelope, an electron gun mounted within said envelope, said gunrbeing adapted to project a nat horizontal beam of electrons, a i'lrst target mounted within said tube, a second target mounted within said tube, a rst mask mounted between the electron gun end of the first target, said mask having means defining openings therein, the horizontal dimension of the openings thus formed increasing within a given range of vertical deflection of the beam and decreasing within ranges adjacent said given range, a second mask mounted between the electron gun and the second target said latter mask having means denning openings therein, the horizontal dimension of the openings thus formed decreasing within said given range of vertical deiiect'ion and increasing within said adjacent ranges, and separate leads connected to each of said targets and extending through said envelope.

l2. A device for transmitting colored images comprising means for generating video signals related to partial images of a plurality of colors of a scanned object, means for developing a voltage wave in response to said video signals that has a plurality of values, certain predetermined groups of these values lying within successive total brightness levels determined by at least two of the partial images as indicated by said signals, the rst and last levels and alternate intermediate levels within at least some of said groups corresponding to combinations of a first set of values of at least two signals, the levels intermediate said latter levels of a given total brightness level being related to combinations of a second set of values of at least two signals.

13. A transmission system for transmitting different values of three primary colors comprising means for deriving a video signal corresponding to a first primary color, means for deriving a video signal corresponding to a second primary color and means for deriving a third signal corresponding to a third primary color, said video signals contemporaneously corresponding to the respective color content at the same point of a scanned object, means for coding the ratio between any two video signals and their Vaccumulated value, means for continuously applying the rst signal to said coding means, and means for successively applying the second and third signals to said coding means.

GEORGE C. SZIKLAI.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,272,638 Hardy Feb. 10, 1942 2,375,966 Valensi May l5, 1945 2,461,515 Bronwell Feb. 15, 1949 2,492,926 Valensi Dec. 27, 1949 FOREIGN PATENTS Number Country Date 505,653 Great Britain May 1l, 1939 524,443 Great Britain Jan. 14, 1939 

